diff --git a/src/main/gtk-3.0/gtk-dark.css b/src/main/gtk-3.0/gtk-dark.css
index 5b62dd19..800393fe 100644
--- a/src/main/gtk-3.0/gtk-dark.css
+++ b/src/main/gtk-3.0/gtk-dark.css
@@ -3302,7 +3302,7 @@ frame > border, .frame {
   border-style: none;
 }
 
-frame.flat > border, statusbar frame > border {
+frame.flat > border, frame > border.flat, statusbar frame > border {
   border: none;
 }
 
diff --git a/src/main/gtk-3.0/gtk-light.css b/src/main/gtk-3.0/gtk-light.css
index 35df4b65..3ffed650 100644
--- a/src/main/gtk-3.0/gtk-light.css
+++ b/src/main/gtk-3.0/gtk-light.css
@@ -3302,7 +3302,7 @@ frame > border, .frame {
   border-style: none;
 }
 
-frame.flat > border, statusbar frame > border {
+frame.flat > border, frame > border.flat, statusbar frame > border {
   border: none;
 }
 
diff --git a/src/main/gtk-3.0/gtk.css b/src/main/gtk-3.0/gtk.css
index 0c749f74..d6778332 100644
--- a/src/main/gtk-3.0/gtk.css
+++ b/src/main/gtk-3.0/gtk.css
@@ -3311,7 +3311,7 @@ frame > border, .frame {
   border-style: none;
 }
 
-frame.flat > border, statusbar frame > border {
+frame.flat > border, frame > border.flat, statusbar frame > border {
   border: none;
 }
 
diff --git a/src/sass/gtk/_common-3.0.scss b/src/sass/gtk/_common-3.0.scss
index 3770b363..5842ded3 100644
--- a/src/sass/gtk/_common-3.0.scss
+++ b/src/sass/gtk/_common-3.0.scss
@@ -2793,6 +2793,7 @@ frame {
   & > border { @extend %frame; }
 
   &.flat > border,
+  & > border.flat,
   statusbar & > border { border: none; } // for backward compatibility
 }